Extension ladders have at least one telescoping or fly extension section that slides relative to a base or base section of a ladder to gain additional length or height that is adjusted by pulling on a rope. In many cases, when using the rope, it can slip from the user's hand, thereby releasing the fly or telescoping section accidentally, causing the fly or telescoping extension section to slide uncontrollably downward, potentially causing serious injury to the user's arm, hand, knee or other parts of the body. Additionally, ladder rails will typically slide apart from each other, or unlock at the rung-locks, when the ladder is set down, dropped, moved, bumped, transported, carried or when the base section slides out and away from a structure supporting the top of the ladder.
Locks are known which prevent the two or more sections from sliding relative to each other when the ladder is fully retracted. The locks cannot be engaged at any point in the travel of the sections relative to each other.